Pulse-Induced Phototropisms in Oat and Maize Coleoptiles

Publisher Website
Google Scholar
Abstract
Phototropisms induced by a pulse (1-30 seconds) of blue light in red-light-grown coleoptiles of oats (Avena sativa L.) and maize (Zea mays L.) were investigated in terms of fluence-response relationships and time courses. Phototropic stimulation was made by a laser beam (457.9 nanometers), allowing application of high-fluence pulses. The phototropic fluence-response curves for oats and maize revealed two peaks in the positive range, thus indicating the occurrence of two separable pulse-induced positive responses. The response at low fluences corresponded to the ''first positive curvature''. The response at high fluences was very small in oats, but was large in maize. Reciprocity was valid in this high-fluence response (tested only for maize), indicating that it is distinct from the so-called ''second positive curvature''. In oats, the trough between the two positive responses fell into the negative range. This negative response, corresponding to the ''first negative curvature'', showed time courses distinct from those of ''first positive curvature:'' the negative response was induced after a longer time lag and developed with a more gradual increase of the rate of bending. The maximal rate of the negative response was as high as one-half of that of first positive curvature. in maize, the trough between the two responses was in the positive range, and the time-course result revealed no apparent response counteracting the positive responses. Physiological and ecological implications of the pulse-induced phototropisms are discussed.